Split gate embedded memory technology and method of manufacturing thereof

ABSTRACT

Semiconductor devices and methods for forming a semiconductor device are disclosed. The method includes providing a substrate prepared with a memory cell region. A first gate structure is formed on the memory cell region. An isolation layer is formed on the substrate and over the first gate structure. A second gate structure is formed adjacent to and separated from the first gate structure by the isolation layer. The first and second gate structures are processed to form at least one split gate structure with first and second adjacent gates. Asymmetrical source and drain regions are provided adjacent to first and second sides of the split gate structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. ProvisionalApplication Ser. No. 61/865,143, filed on Aug. 13, 2013, which is hereinincorporated by reference in its entirety.

BACKGROUND

Non-volatile memory (NVM) devices are able to retain stored data evenwhen the power supply is interrupted. NVM devices can be programmedusing electrical signals. For the embedded memory device to bebyte-operational, a two-transistor (2T) cell structure which includes amemory transistor such as silicon-oxide-nitride-oxide-silicon (SONOS)type and a select or access transistor in series can be provided. Thememory transistor stores data programmed into the memory cell while theaccess transistor selects the memory cell to be programmed or erased.However, 2T cell structure requires a lot of space. Split gate NVMdevices are proposed to offer a high density solution which requiresless space, low cost, re-programmable in system, and highly reliable.

However, the 2T cell structure and current split gate NVM devices sufferseveral limitations, such as scalability issues or program disturbance.Further, there is also a desire to form split gate memory devices whichcan be integrated together with other types of devices, such as lowvoltage (LV), medium voltage (MV) and high voltage (HV) devices, to formembedded memory in a cost effective manner. As such, it is desirable toprovide a split gate NVM cell with improved scalability, increasedprogram/erase speed, minimized program disturbance and with improvedendurance and a low cost methodology which can integrate logic andmemory devices on the same chip.

SUMMARY

Embodiments generally relate to semiconductor devices. In oneembodiment, a method for forming a semiconductor device is disclosed.The method includes providing a substrate prepared with a memory cellregion. A first gate structure is formed on the memory cell region. Anisolation layer is formed on the substrate and over the first gatestructure. A second gate structure is formed adjacent to and separatedfrom the first gate structure by the isolation layer. The first andsecond gate structures are processed to form at least one split gatestructure with first and second adjacent gates. Asymmetrical source anddrain regions are provided adjacent to first and second sides of thesplit gate structure.

In another embodiment, a semiconductor device is presented. The deviceincludes a substrate having a memory cell region. A first gate isdisposed on the memory cell region. An isolation layer is disposed onthe substrate and over the first gate. A second gate is adjacent to andseparated from the first gate by the isolation layer and the first andsecond gates correspond to a split gate structure. The device alsoincludes asymmetrical source and drain regions adjacent to first andsecond sides of the split gate structure.

These and other advantages and features of the embodiments hereindisclosed, will become apparent through reference to the followingdescription and the accompanying drawings. Furthermore, it is to beunderstood that the features of the various embodiments described hereinare not mutually exclusive and can exist in various combinations andpermutations.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. Various embodiments of theinvention are described with reference to the following drawings, inwhich:

FIG. 1 a shows an embodiment of a portion of a device;

FIGS. 1 b-1 c show various embodiments of a memory array;

FIGS. 2-3 show various embodiments of a portion of a device;

FIGS. 4 a-4 h show an embodiment of a process for forming asemiconductor device;

FIGS. 5 a-5 g show another embodiment of a process for forming asemiconductor device; and

FIGS. 6 a-6 f show yet another embodiment of a process for forming asemiconductor device.

DETAILED DESCRIPTION

Embodiments generally relate to semiconductor devices and fabricatingsemiconductor devices. Some embodiments relate to memory devices, suchas NVM devices. Such memory devices, for example, can be incorporatedinto standalone memory devices or easily integrated into logicprocessing technologies to form integrated circuits (ICs) withoutcompromising the reliabilities of the different devices. Such ICs may beused in, for example, embedded flash technology or other types oftechnology. The ICs can be incorporated into or used with, for example,microcontrollers for automotive, communication systems, and for consumerproducts such as cell phones, memory cards, smart cards, internet ofthings (IOT), etc.

FIG. 1 a shows an embodiment of a portion 100 a of a device. As shown,the portion includes a substrate 101. The substrate includes asemiconductor substrate, such as silicon. Other types of semiconductorsubstrates, for example, SiGe, SiGeC, SiC, silicon-on-insulators (SOIs),SiGe-on-insulators (SGOIs), are also useful. The substrate, for example,includes a lightly doped substrate. The substrate may be lightly dopedwith first type dopants. The first type dopants, for example, includep-type dopants, forming a lightly-doped p-type substrate. Providingother types of substrates may also be useful. For example, the substratemay be doped with second type dopants, such as n-type dopants and/orother dopant concentrations, including intrinsically doped substrates.

The substrate can be prepared with a region 108 containing memory cells.In one embodiment, the memory cells include NVM cells. Other types ofmemory cells are also useful. The region can be referred to as an arrayregion. The array region shows one memory cell 198. Although only onememory cell is shown, it is understood that a plurality of memory cellscan be included in the device. The array region can be arranged to havesub-regions corresponding to, for example, groups of memory cells. Thearray region includes heavily doped well 118 or wells with dopants of afirst polarity type. In one embodiment, the doped well 118 includesdopant concentration of about 1E16-1E17 cm⁻³. Other dopant concentrationmay also be useful. The first polarity type wells are used for secondpolarity type memory cells. For example, p-type wells are used forn-type memory cells while n-type wells are used for p-type memory cells.P-type dopants can include boron (B), BF₂, indium (In) or a combinationthereof while n-type dopants can include phosphorus (P), arsenic (As),antimony (Sb) or a combination thereof. An optional deep well 111 ahaving second polarity type dopants may also be included in thesubstrate to isolate the doped well 118 from the substrate 101.

Additionally, the substrate may include non-array regions (not shown),such as logic and peripheral regions. The logic and peripheral regions,for example, can include low voltage (LV), medium voltage (MV) and highvoltage (HV) regions. For example, the LV region is suitable for 1.2 VLV transistors; the MV region is suitable for 5.0-7.0 V MV transistorswhile the HV region is suitable for over 15 V HV transistors. Othersuitable voltage ranges may also be useful, depending on devicerequirements. The substrate may also include other regions for othertypes of circuitry, depending on the type of device or IC applications.

The substrate includes isolation regions 110 a to isolate active deviceregions from other active device regions, as required. The isolationregions, for example, include shallow trench isolation (STI) regions.Other types of isolation regions are also useful.

In one embodiment, the memory cell includes a split gate transistor. Thesplit gate transistor, in one embodiment, includes first and secondgates 138 and 133. For example, the first gate 138 can be a select gateand the second gate 133 can be a control gate. In one embodiment, thefirst and second gates are adjacent gates disposed on the surface of thesubstrate 101 a. The width of the select gate, for example, is about 100nm, depending on the technology node. Other suitable width dimensionsmay also be useful. As shown in FIG. 1 a, the first and second gateshave non-coplanar top surfaces. For example, the control gate 133 can beadjacent to and overlaps the select gate 138. In one embodiment, thecontrol gate is adjacent to and overlaps a portion of the select gate,leaving a portion of the select gate uncovered by the control gate in anon-overlap region. As shown, another portion of the control gate isdisposed over the substrate. In one embodiment, the width of the overlapportion of the control gate over the select gate is about 20 nm whilethe width of the portion of the control gate above the substrate isabout 100 nm. Other suitable width dimensions may also be useful.

The split gate transistor includes a first gate dielectric 124. Thefirst gate dielectric 124, for example, serves as the select gatedielectric. The select gate dielectric 124 separates the select gate 138from the substrate 101. The select gate dielectric, for example,includes silicon oxide. The thickness of the select gate dielectric, forexample, is about 125 Å. Other suitable dielectric materials andthickness dimensions for the select gate dielectric may be used as longas it is sufficiently thick and suitable for use for MV application. Theselect and control gates are isolated from each other and the substrateby an isolation layer 148. The isolation layer, in one embodiment,includes a composite layer stack. In one embodiment, the composite layerstack includes an oxide-nitride-oxide (ONO) stack. In such case, thememory cell is a split-gate SONOS memory cell. The physical thickness ofthe lower oxide layer, for example, may be about 60 Å, the thickness ofthe nitride layer, for example, may be about 70 Å while the top or upperoxide layer of the ONO stack includes a thickness of about 60 Å. Othersuitable thicknesses may also be useful. The isolation layer may includeother suitable isolation material. For example, the middle nitride layerof the ONO stack may be replaced by high-K dielectric materials such asAl₂O₃, HbOx, TaOx and others. In one embodiment, the isolation layer 148may also serve as a charge storage layer.

In one embodiment, the split gate transistor includes a hard mask 417.The hard mask, for example, includes an anti-reflective coating (ARC)layer. The ARC layer, for example, includes silicon rich nitride ARC.Other suitable types of hard mask or ARC layers are also useful. The ARClayer, for example, includes a thickness of about 50 Å. Otherthicknesses may also be useful so long as it is sufficiently thick toserve as an etch stop layer as well as to elevate the height of thecontrol gate such that larger spacer can be formed later to avoidshorting between the select and control gates. First and second sidewallspacers 172 and 174 can be provided on sidewalls of the gates. The firstsidewall spacers, for example, include oxide while the second sidewallspacers 174 include nitride. Other suitable dielectric materials mayalso be used. The first sidewall spacers, for example, may be L-shapedsidewall spacers. Other suitable shapes may also be useful. Althoughfirst and second sidewall spacers are shown, it is understood that thememory cell may include only the first or second sidewall spacers.

The control gate, for example, may be a gate conductor which serves as acommon gate for a row of memory cells. Adjacent memory cells can beconfigured as mirror gate electrodes which may share a common diffusionregion. For example, adjacent memory cells can be configured as mirrorgate electrodes which may share a common source region 168. Otherconfigurations or layouts of memory cells are also useful. The gates mayalso be provided with silicide contacts (not shown).

In one embodiment, the split gate transistor is disposed between firstand second terminals. The terminals can include, for example, heavilydoped diffusion regions 168. The first terminal 168 adjacent to theselect gate, for example, serves as a heavily doped drain region and thesecond terminal 168 adjacent to the control gate serves as a heavilydoped source region. The heavily doped source and drain (S/D) regions,for example, include second polarity type dopants for second polaritytype memory cell. The heavily doped S/D regions, for example, includesecond type dopants, such as n-type dopants, having a dopantconcentration of about 10¹⁹-10²⁰ atom/cm³ and to a depth of about a fewthousand Å from the first substrate surface. Other concentrations ordepth dimensions may also be useful. In one embodiment, the heavilydoped S/D regions 168 include the same dopants. For example, the heavilydoped S/D regions include arsenic (As). The memory cell may also includean extension or lightly doped diffusion (LDD) region 158 which isshallower and extends underneath the spacer adjacent to the edge of theselect gate 138. The LDD region 158, for example, includes second typedopants as extension implant such as phosphorus (P) having a dopantconcentration of about 10¹⁷ atom/cm³ and to a depth of about 3000-4000 Åfrom the first substrate surface. In some cases, the LDD region mayincorporate low dose of boron (B) as halo implant to suppress shortchannel effect.

In one embodiment, the memory cell also includes counter doped regions128. The counter doped regions include dopants which are the samepolarity type as the dopants of the lightly doped region 158. Thecounter doped regions are formed adjacent to the sides of the selectgate and under the control gate by blanket implant with no addedlithographic mask. In one embodiment, the counter doped regions may belightly to intermediately doped like the LDD region 158 but with a depthshallower than the LDD region. For example, the counter doped regionincludes phosphorus (P) having dopant concentration of about 10¹⁷atoms/cm³ and the depth of the counter doped regions may be about 2000 Åfrom the substrate surface 101 a. Other dopant concentrations and depthdimensions may also be useful. By providing counter doped regions, thememory cell 198 allows asymmetrical S/D regions or junctions to beformed with only the use of a single mask and optimize individualthreshold voltage (Vth) for the select gate portion to improve the shortchannel effect (SCE) and the control gate portion to improve theprogramming efficiency.

Referring to FIG. 1 a, an interlevel dielectric (ILD) layer 181 isprovided over the substrate. Silicide contacts (not shown) and contacts183 are provided, coupling the diffusion regions to source lines (SLs),bit lines (BLs), and gate electrodes to select gate lines (SGLs),control gate lines (CGLs). The SGL and the CGL forms a word line (WL) ina row direction while the SL and the BL are disposed in a columndirection. The silicide contacts, for example, include nickel or cobaltbased silicide contacts while the contacts 183 include tungstencontacts. Other suitable materials may also be used. As shown, the drainregion 168 is coupled to the BL, the select gate electrode 138 iscoupled to the SGL, the control gate electrode 133 is coupled to the CGLwhile the source region 168 is coupled to the SL.

FIG. 1 b shows an embodiment of a memory array 100 b. In one embodiment,the memory array includes a NVM array. The memory array includes aplurality of memory cells arranged in rows and columns. The memorycells, for example, include memory cells 198 as described in FIG. 1 a. Arow corresponds to, for example, a SGL and a CGL which also serve as awordline (WL) and a column corresponds to a bitline (BL) of the array.In one embodiment, the BLs are coupled to the drain regions adjacent tothe select gates while WLs are coupled to the select gate and controlgates of the memory cells. For example, WLs provide VCG, SGLs may beused to provide VSG to the select gates of the memory cells and BLsprovide VD. Source lines (SLs) may not be common to the cells ofdifferent sectors. The SLs may be employed to provide Vs to the sourceregions adjacent to the control gates. SLs and SGLs may be coupled tothe memory cells as desired. The memory cells may be configured in a NORtype array architecture within a sector. The configuration as shown inFIG. 1 b, for example, allows for standard or drain sensing with commonsource within a sector and different source bias across sectors. Suchconfiguration has its benefits, such as reducing the gate disturbedcells during program operation when drain or bit line inhibit voltagesare applied for all unselected (unsel.) BLs in the selected (sel.)sector. The gate disturbed cells are defined as the cells sharing thesame selected WLs during program operation. Furthermore, the memory cellwill not suffer punch-through issues. A new SLs driver may be requiredfor this configuration.

FIG. 1 c shows another embodiment of a memory array 100 c. The memoryarray 100 c is similar to the memory array 100 b as described in FIG. 1b. In the interest of brevity, common elements with the same referencenumerals may not be described or described in detail. In one embodiment,the SLs are coupled to the source region adjacent to the select gatewhile BLs are coupled to the drain region adjacent to the control gate.The configuration as shown in FIG. 1 c allows for source sensing in aNOR type array architecture in which source line is common to allsectors. In this configuration, SLs driver is not required, resulting insmaller NVM macro size. Further, this configuration provides improvedmemory cells leakage control when unselected CGLs bias to some positivevoltage values.

A memory cell may be accessed by applying appropriate voltages to theterminals. By applying appropriate voltages to the CGL, SGL, SL and BL,a bit or multiple bits of the memory array may be selected foraccessing. A memory access may include a program, read or eraseoperation. Table 1 below shows various signals applied to the terminalsof a memory array of FIG. 1 b or FIG. 1 c of selected (sel.) andnon-selected (non-sel.) cells for the different memory operations:

Erase (F-N) Terminals Operations Read Program tunneling CGL Sel. 1.8 V<9 V ~10 V Non-Sel. 0 V 0 V 0 V SGL Sel. 1.8 V ~1.8 V 0 V Non-Sel. 0 V 0V 0 V SL Sel. 0 V 4 V 0 V Non-Sel. 0.5 V 0 V 0 V BL Sel. 0.5-1 V 10 μA 0V Non-Sel. 0 V 4 V 0 V

The voltage values presented in Table 1 above are exemplary voltagevalues. It is understood that other suitable types of voltage values mayalso be useful, depending on the technology node.

The embodiment described in FIG. 1 a offers several advantages. Thememory cell 198 as described is a split gate transistor having a controlgate adjacent to the select gate and partially overlapping the selectgate, forming a 1.5 transistor (1.5T) cell structure which is smallerthan conventional 2T cell structure. Thus, the memory cell 198 requiresless cell area relative to conventional 2T cell structure. Unlikeconventional SONOS cell which uses Fowler-Nordheim (F-N) tunneling forprogramming, the memory cell 198 is a split-gate SONOS cell which adoptschannel hot electron (CHE) for programming, but with reduced programmingcurrent by 10 times by using a technique unique to the 1.5T cellstructure such as source-side injection (SSI). For example, a strongelectric field near the source side of the device such that highefficient hot electron injection occurs near the source under the highcontrol gate bias but simultaneously limited the channel current whichflows between source and drain regions under the weak select gate biasvoltage. Thus, the programming time can be reduced to be 10 μs or lesswhich is faster than conventional SONOS cell. Further, since hotelectron injection is used for programming which is less dependent ongate oxide, there is no need for an ultra-thin tunnel oxide growing fromthe silicon substrate. This eliminates the manufacturability problem oftraditional SONOS device. Moreover, the erase operation of the memorycell 198 is achieved by tunneling electrons through the top oxide of theONO stack. Since the thin top oxide is grown from the nitride layer, theself-saturated nature of the top oxide growth makes the thicknesscontrol more practical. Moreover, shorter erase time is achieved.Further, as shown, the source region adjacent to the control gate isdevoid of LDD region while the drain region adjacent to the drain regionincludes the LDD region, forming asymmetrical S/D regions. As described,by providing counter doped regions, the memory cell 198 allows theasymmetrical S/D regions or junctions to be formed with only one maskand optimize individual Vth for the select gate portion to improve theshort channel effect (SCE) and the control gate portion to improve theprogramming efficiency.

FIG. 2 shows another embodiment of a portion of a device 200. Theportion of the device 200 includes a memory cell pair. For example, theportion of the device 200 includes first and second memory cells 298 ₁and 298 ₂. Although a memory cell pair is shown, it is understood thatthe memory cell region may include one or more than two memory cells.The memory cell 298 is similar to the memory cell 198 as described inFIG. 1 a. In the interest of brevity, common elements with the samereference numerals may not be described or described in detail.

The memory cell 298 includes a split-gate transistor. The split-gatetransistor includes first and second gates 138 and 233. The first gate138 serves as the select gate and the second gate 233 serves as thecontrol gate. As shown, the control gate 233 is disposed adjacent to theselect gate 138 and is separated from each other and the substrate by anisolation layer 148. The split gate transistor is disposed between firstand second terminals. The first terminal which is disposed adjacent tothe control gate 233, for example, serves as the source region while thesecond terminal which is disposed adjacent to the select gate 138, forexample, serves as the drain region. In one embodiment, the first andsecond memory cells 298 ₁ and 298 ₂ share a common second terminal. Forexample, the first and second memory cells 298 ₁ and 298 ₂ share acommon drain region.

In one embodiment, the S/D regions include asymmetrical S/D regions. TheS/D regions, for example, include heavily doped and lightly dopedregions. The heavily doped S/D regions 168 as shown in FIG. 2 areidentical to the heavily doped S/D regions 168 as shown in FIG. 1 a. Forexample, the heavily doped S/D regions 168 include second type dopantshaving a dopant concentration of about 10¹⁹-10²⁰ atom/cm³ and to a depthof about a few thousand Å from the first substrate surface. Otherconcentrations or depth dimensions may also be useful. In oneembodiment, the lightly doped source region 258 and lightly doped drainregion 158 are formed by different dose or energy to produceasymmetrical S/D regions or junctions. For example, low energy and dosesuch as 30-40 keV and 10¹⁷ atoms/cm³ are employed to form a shallowlightly doped drain region 158 while high energy and dose such as 50-60keV and 10¹⁷ atoms/cm³ are used to form deeper lightly doped sourceregion 258 to optimize device performance. Other suitable dose andenergy parameters may also be useful.

As shown in FIG. 2, the first and second gates have non-coplanar topsurfaces. The control gate 233, in one embodiment, differs from thecontrol gate 133 of FIG. 1 a. The control gate 233, in one embodiment,is a control gate spacer. The control gate spacer, for example, includesa width which is about sub-critical dimension (sub-CD), depending on,for example, height of the control gate, deposition and reactive ionetch used for forming the control gate spacer. The width of the controlgate 233, for example, is about less than 100 nm. Other suitable widthdimensions may also be useful. As shown, the control gate 233 isdisposed over the substrate adjacent to the select gate 138 but does notoverlap the select gate 138. As shown in FIG. 2, sidewall oxide 572 andfirst and second sidewall spacers 172 (not shown) and 174 can beprovided on sidewalls of the gates. The sidewall oxides 572, forexample, are formed by thermal oxidation of the select and control gateswhile the first and second sidewall spacers 172 and 174 are logicsidewall spacers that include oxide and nitride as described in FIG. 1a. The sidewall oxides 572, for example, are formed on exposed selectand control gates while the logic sidewall spacers 172 (not shown) and174 are formed over the sidewall oxides 572.

Referring to FIG. 2, an ILD layer 181 is provided over the substrate.Silicide contacts 531 and contacts 183 are provided, coupling thediffusion regions and gate electrodes to SLs, BLs, SGLs, CGLs or WLs,etc. The silicide contacts 531, for example, include nickel basedsilicide contacts and the contacts 183, for example, include tungsten.Other suitable types of materials may also be used.

The embodiment as described in FIG. 2 may offer the same or similaradvantages as described with respect to the embodiment as described inFIG. 1 a. In addition, as described, the control gate 233 is a controlgate spacer. This allows the memory cell of FIG. 2 to be shrunk furtherrelative to the memory cell 198 as described in FIG. 1 a. The memorycell of FIG. 2 also forms asymmetrical S/D regions. As described, thesource and drain regions include same dopants of the second polaritytype with different dose and energy. This allows programming to beperformed at the source side while read operation to be performed at thedrain side. Further, asymmetrical S/D region also enables the selectgate length to be shrunk further, enabling a smaller device to beformed.

FIG. 3 shows another embodiment of a portion of a device 300. Theportion of the device 300 includes a memory cell pair. For example, theportion of the device 300 includes first and second memory cells 398 ₁and 398 ₂. Although a memory cell pair is shown, it is understood thatthe memory cell region may include one or more than two memory cells.The memory cell 398 is similar to the memory cell 198 or 298 asdescribed in FIG. 1 a or FIG. 2. In the interest of brevity, commonelements with the same reference numerals may not be described ordescribed in detail.

The memory cell 398 includes a split gate transistor. The split gatetransistor includes first and second gates 138 and 333. The first gate138 serves as the select gate and the second gate 333 serves as thecontrol gate. As shown, the control gate 333 is disposed adjacent to theselect gate 138 and is separated from each other and the substrate by anisolation layer 148. The split gate transistor is disposed between firstand second terminals. The first terminal which is disposed adjacent tothe control gate 333, for example, serves as the source region while thesecond terminal which is disposed adjacent to the select gate 138, forexample, serves as the drain region. In one embodiment, the first andsecond memory cells 398 ₁ and 398 ₂ share a common second terminal. Forexample, the first and second memory cells 398 ₁ and 398 ₂ share acommon drain region. Similar to the memory cell 298 of FIG. 2, thememory cell 398 also includes asymmetrical S/D regions. For example, thedrain region includes shallow drain region 158 which is formed bydifferent energy and dose than that of the lightly doped source region258.

The control gate 333, in one embodiment, differs from the control gate133 of FIG. 1 a and control gate 233 of FIG. 2. As shown in FIG. 3, thefirst and second gates have substantially coplanar top surfaces. Thecontrol gate 333, in one embodiment, is a control gate spacer havingsubstantially coplanar top surface with the top surface of the selectgate. The control gate spacer 333, for example, includes a width whichmay be about sub-critical dimension (sub-CD), depending on, for example,height of the control gate, deposition and reactive ion etch used forforming the control gate spacer. The width of the control gate 333, forexample, is about 100 nm or less. Other suitable width dimensions mayalso be useful. As shown, the control gate 333 is disposed over thesubstrate adjacent to the select gate 138 but does not overlap theselect gate 138.

In one embodiment, a contact plug 633 is disposed directly over andcoupled to the drain region. In one embodiment, this contact plug 633 ismade borderless to the drain region 268 and is self-aligned to the drainregion. The contact plug 633, in one embodiment, is a borderless dummycontact plug. The dummy contact plug, for example, includes polysilicon.Other suitable materials may also be used as the contact plug. The sizeof the contact plug 633, in one embodiment, is less than 2f, where f isthe minimum technology node feature size. For example, the width of theborderless contact plug, for example, is at or below 1.5f. In oneembodiment, the contact plug 633 is isolated from the select gates 138by insulator liners 631. In one embodiment, the insulator liners 631include a dielectric material such as ozone-tetraethoxysilane(ozone-TEOS) or high aspect ratio process (HARP) dielectric material.Other suitable types of dielectric materials may also be used as theinsulator liners.

Referring to FIG. 3, an interlevel dielectric (ILD) layer 181 isprovided over the substrate. Silicide contacts 531 and contacts 183 areprovided, coupling the diffusion regions and gate electrodes to SLs,BLs, SGLs, CGLs or WLs, etc. In addition, unlike the memory cell of FIG.2, the contact 184 over the drain region 268 of FIG. 3 is indirectlycoupled to the drain region 268 through the contact plug 633.

The embodiment as described in FIG. 3 may offer the same or similaradvantages as described with respect to the embodiments as described inFIGS. 1 a and 2. Additionally, the use of the insulator liners 631 whichenables a contact plug 633 to be made borderless and self-aligned to thedrain region as shown in FIG. 3 removes 2 times the space (2f; f=minimumtechnology node feature size) required if contact 183 were made directlyto the drain region using lithographic technique as shown in FIG. 2. Forexample, the borderless contact plug allows the spacing of adjacentselect gates to be minimized and not restricted by lithographiclimitations. This enables the memory cell to shrink further with about10-15% reduction in cell size.

The memory cell 298 and 398 may also be used in the memory arrayconfiguration as that presented in FIGS. 1 b and 1 c. Thus, details ofthe memory array using the memory cell 298 and 398 will not be describedor described in detail.

FIGS. 4 a-4 h illustrate an embodiment of a process 400 for forming asemiconductor device. The process 400 as will be described is highlycompatible with complementary metal oxide semiconductor (CMOS) logicprocessing technology. Referring to FIG. 4 a, a substrate 101 isprovided. The substrate includes a semiconductor substrate, such assilicon. Other types of semiconductor substrates, for example, SiGe,SiGeC, SiC, silicon-on-insulators (SOIs), SiGe-on-insulators (SGOIs),are also useful. The substrate, for example, includes a lightly dopedsubstrate. The substrate may be lightly doped with first type dopants.The first type dopants, for example, include p-type dopants, forming alightly-doped p-type substrate. Providing other types of substrates mayalso be useful. For example, the substrate may be doped with second typedopants, such as n-type dopants and/or other dopant concentrations,including intrinsically doped substrates.

As shown, the substrate is prepared with first, second, third and fourthregions. In one embodiment, the first region 102, for example, includesa low voltage (LV) device region of which LV devices are to be formed.As shown, the first region includes first 102 ₁ and second 102 ₂sub-regions. The second region 104, for example, includes a mediumvoltage (MV) device region of which MV devices are to be formed. Similarto the first region, the second region also includes first 104 ₁ andsecond 104 ₂ sub-regions. The third region 106, for example, includeshigh voltage (HV) device region on which HV devices are to be formed.The third region, as shown, includes first 106 ₁ and second 106 ₂sub-regions. The fourth region 108 includes a memory cell region. Asshown, the memory cell region is provided on the substrate on which atleast one memory cell is to be formed. The memory cell region, forexample, is a part of an array region with a plurality of cell regionson which memory cells are formed to create a memory array.Illustratively, the substrate is provided with one LV region, one MVregion, one HV region and one memory cell region. The LV, MV and HVregions may collectively be referred to as the logic and peripheralregions. Providing a substrate with other numbers of regions orsub-regions may also be useful.

The substrate is prepared with isolation regions 110, such as shallowtrench isolation (STI) regions or deep trench isolation (DTI) regions.First type isolation regions 110 a are used for separating the differentwell regions to provide minimum spacing of any given active regionsbetween adjacent wells. Second type isolation regions 110 b, forexample, may also be used for separating 2 active regions within thesame well with minimum spacing. For example, the second type isolationregion may be used to provide isolation of source to drain with the samedevice when the device is electrically on very high HV gate or drainbias. Various processes can be employed to form the isolation regions.For example, first and second pad layers (not shown) may be provided ontop of the substrate. The first pad layer, for example, includes a padoxide layer while the second pad layer includes a pad nitride layer. Thesubstrate is etched using etch and mask techniques to form trencheswhich are then filled with dielectric material such as silicon oxide.Excess dielectric material is removed by, for example, chemicalmechanical polishing (CMP), producing isolation structures having topsurfaces co-planar with the second pad layer. In one embodiment, thefirst and second pad layers are removed, producing isolation structureshaving surfaces which are non co-planar with a first substrate surface.Other processes or materials can also be used to form the isolationregions.

The process may continue to form various wells in the substrate. Forexample, the substrate 101 is implanted with dopants to form deep wells.The substrate, for example, is implanted with second polarity typedopants, such as n-type dopants, in LV and MV regions 102 and 104, firstsub-region of the HV region 106 ₁ and memory cell region 108 to formsecond polarity type deep wells 111 a while covering the secondsub-region 106 ₂ of the HV region using a deep well implant mask (notshown). In one embodiment, n-type dopants, such as phosphorus, areimplanted into the substrate. The process may also continue to implantfirst polarity type dopants, such as p-type dopants in the secondsub-region 106 ₂ of the HV region to form first polarity type deep well111 b while covering the other regions using another deep well implantmask (not shown). In one embodiment, p-type dopants, such as boron, areimplanted into the substrate. The deep wells, for example, are implantedwith first or second polarity type dopants having a dopant concentrationof about 10¹⁶-10¹⁸ atom/cm³ and to a depth of about 1.5-2.2 μm from thefirst substrate surface 101 a. Providing other types of dopants,concentration and depths using suitable implant masks, dose and energyto form the deep wells may also be useful.

The process also forms a LV well region of the second polarity type 112a, such as n-type, in the first sub-region 102 ₁ and a LV well region ofthe first polarity type 112 b, such as p-type, in the second sub-region102 ₂ in the LV region 102. The LV wells, for example, are implantedwith first or second polarity type dopants having a dopant concentrationof about 10¹⁵-10¹⁷ atom/cm³ and to a depth of about 0.3-0.4 μm from thefirst substrate surface 101 a. MV well regions are also formed in the MVregion 104. For example, a MV well region of the second polarity type114 a, such as n-type, is formed in the first sub-region 104 ₁ and a MVwell region of the first polarity type 114 b, such as p-type, is formedin the second sub-region 104 ₂ in the MV region 104. The MV wells, forexample, are implanted with first or second polarity type dopants havinga dopant concentration of about 10¹⁶-10¹⁸ atom/cm³ and to a depth ofabout 0.5-1 μm from the first substrate surface 101 a. Further, theprocess also forms HV well regions in the HV region 106. For example, aHV well region of the first polarity type 116 a, such as p-type, isformed in the first sub-region 106 ₁ and a HV well region of the secondpolarity type 116 b, such as n-type, is formed in the second sub-region106 ₂ in the HV region 106. The HV wells, for example, are implantedwith first or second polarity type dopants having a dopant concentrationof about 10¹⁶-10¹⁸ atom/cm³ and to a depth of about 1-1.5 μm from thefirst substrate surface 101 a. Providing other types of dopants,concentration and depths using suitable implant masks to form the LV, MVand HV wells may also be useful.

Referring to FIG. 4 a, a soft mask layer (not shown) is provided overthe substrate. The soft mask is patterned to form an opening to exposethe memory cell region 108. In one embodiment, the opening correspondsto the opening for a memory cell well implant. For example, the softmask serves as the memory cell well implant mask. As shown in FIG. 4 a,the substrate is implanted with first type dopants to form a first typememory cell well 118 for a second polarity type memory cell. Forexample, p-type dopants, such as boron, are implanted into the substrateto form a p-type memory cell well for a n-type memory cell. The memorycell well, for example, is implanted with p-type dopants having a dopantconcentration of about 10¹⁶-10¹⁷ atom/cm³ and to a depth of about 0.5-1μm from the first substrate surface. Providing other suitable types ofdopants, concentration and depths to form the memory cell well may alsobe useful.

A first gate dielectric layer 126 is formed over the substrate. In oneembodiment, the first gate dielectric layer includes an oxide layer. Theoxide layer includes silicon oxide. Other types of dielectric materialsmay also be used to form the first gate dielectric layer. Alternatively,high-k or low-k or composite dielectric materials may be used. Thethickness of the first gate dielectric layer may be about 750 Å. Othersuitable thicknesses may also be useful as long as it is sufficientlythick and suitable for use as HV gate dielectric. In one embodiment, thefirst gate dielectric layer is formed on the entire surface of thesubstrate. In one embodiment, the first gate dielectric layer is formedby CVD TEOS or furnace high temperature oxide (HTO) deposition. Othersuitable techniques may also be used to form the first gate dielectriclayer.

The process continues to remove portions of the first gate dielectriclayer 126 over the MV and memory cell regions 104 and 108. The portionsof the first gate dielectric layer are removed by mask and etchtechniques. Removal can be achieved using, for example, an anisotropicetch such as reactive ion etch (RIE). Other suitable removal techniquesmay also be employed. The process continues to form second gatedielectric layer 124 over the MV and memory cell regions 104 and 108. Inone embodiment, the second gate dielectric layer includes an oxidelayer. The oxide layer includes silicon oxide. Other types of dielectricmaterials may also be used to form the second gate dielectric layer.Alternatively, high-k or low-k or composite dielectric materials may beused. The thickness of the second gate dielectric layer may be about 125Å. Other suitable thicknesses may also be useful as long as it issufficiently thick and suitable for use as MV gate dielectric. In oneembodiment, the second gate dielectric layer is formed by furnace orin-situ steam generated (ISSG) oxidation. Other suitable techniques mayalso be used to form the second gate dielectric layer. The second gatedielectric layer 124 formed in the MV region serves as gate dielectricfor the MV devices to be formed later while the second gate dielectriclayer 124 formed in the memory cell region, for example, serves as theselect gate dielectric of a select gate which will be described later.

The process continues to remove portion of the first gate dielectriclayer over the LV region 102. The portion of the first gate dielectriclayer in the LV region is removed by mask and etch techniques. Removalcan be achieved using, for example, an anisotropic etch such as RIE.Other suitable removal techniques may also be employed. The processcontinues to form third gate dielectric layer over the LV region. In oneembodiment, the third gate dielectric layer includes an oxide layer. Theoxide layer includes silicon oxide. Other types of dielectric materialsmay also be used to form the third gate dielectric layer. Alternatively,high-k or low-k or composite dielectric materials may be used. Thethickness of the third gate dielectric layer may be about 20-30 Å. Othersuitable thicknesses may also be useful as long as it is sufficientlythick and suitable for use as LV gate dielectric 122. In one embodiment,the third gate dielectric layer is formed by nitrided oxide. Othersuitable techniques may also be used to form the third gate dielectriclayer. As shown in FIG. 4 a, the substrate is prepared with varying gatedielectric thickness over the various regions. The LV region includesthe thinnest gate dielectric while the HV region includes the thickestgate dielectric.

The process continues to form a first gate electrode layer 430 on thegate dielectric layers. The first gate electrode layer includes, in oneembodiment, polysilicon. Other types of gate electrode materials arealso useful. The thickness of the first gate electrode layer, forexample, may be about 1000 Å. Other thicknesses are also useful. Varioustechniques can be used to form the first gate electrode layer. Forexample, polysilicon can be formed by chemical vapor deposition (CVD).Other techniques, depending on the material, may also be useful.

A mask layer 411, such as a photoresist, is formed on the substrate. Themask layer includes an opening which exposes the memory cell region 108while covering the other regions. In one embodiment, the exposed portionof the first gate electrode layer in the memory cell region can beimplanted or in-situ doped with dopants such as phosphorous to form adoped gate electrode layer. The exposed portion of the first gateelectrode layer in the memory cell region, for example, is implantedwith phosphorous dopants having a dopant concentration of about 10²⁰atom/cm³. Other suitable types of dopants and dopant concentrations mayalso be useful so long as it prevents poly depletion, reduce resistanceand reduces voltage drop.

The process continues to form select gate 138 of the memory cell. A masklayer (not shown), such as a photoresist, is formed on the substrate. Ahard mask layer 417, such as an anti-reflective coating (ARC) layer maybe provided between the mask and first gate electrode layer. In oneembodiment, the ARC layer is a Si-rich ARC layer. Other suitable typesof hard mask or ARC layers may also be useful. The mask is patterned asdesired to serve as a select gate mask. For example, the mask ispatterned to expose portions of the first gate electrode layer in thememory cell region to be removed. The select gate mask protects portionsof the first gate electrode layer and hard mask layer over the otherregions. As such, the exposed portions of the first gate electrode layerand hard mask layer over the memory cell region are removed. Removal ofthe exposed portions can be achieved using, for example, RIE. Othertechniques may also be useful. The portion of the first gate electrodelayer and the hard mask layer protected by the mask layer in the memorycell region remains. The remaining portion of the first gate electrodelayer in the memory cell region serves as the select gate electrode 138.The width of the select gate electrode (W_(SL)), for example, is about100 nm, depending on technology node. Other suitable width dimension mayalso be useful.

The process continues to form counter doped regions 128 in the memorycell region. In one embodiment, the counter doped regions are formed byblanket implanting second polarity type dopants into regions adjacent tosides of the select gate and under the control gate which will be formedlater. As shown, the counter doped regions are formed adjacent to sidesof the select gate and under the control gate with no added lithographicmask. The counter doped regions include dopants which are the samepolarity type as the dopants of the source/drain (S/D) regions whichwill be formed later. The counter doped regions are formed adjacent tothe sides of the select gate within the memory cell well 118 havingfirst polarity type dopants. In one embodiment, the counter dopedregions may be a lightly to intermediately doped region. For example,the counter doped regions include dopants such as phosphorus (P) havingdopant concentration of about 10¹⁷ atoms/cm³ and the depth of thecounter doped regions may be about 2000 Å from the substrate surface 101a. Other dopant concentrations and depth dimensions may also be useful.In some embodiments, an anneal may be performed to diffuse the dopants.Other techniques for forming the counter doped regions may also beuseful.

The process continues to form an isolation layer 448 over the substrateas shown in FIG. 4 c. Typically, the isolation layer is formed as ablanket layer on the substrate. The isolation layer, in one embodiment,includes a composite layer stack. In one embodiment, the composite layerstack includes an oxide-nitride-oxide (ONO) stack. Various techniquescan be used to form the ONO stack. In one embodiment, a lower oxidelayer is first formed. The lower oxide layer can be formed by, forexample, high temperature oxidation (HTO). Other techniques including,for example, low pressure CVD (LPCVD) and thermal oxidation are alsouseful. The physical thickness of the lower oxide layer, for example,may be about 60 Å. Next, a nitride layer is deposited. The thickness ofthe nitride layer, for example, may be about 70 Å. The nitride layer canbe formed by LPCVD. Other techniques are also useful. Finally, the topor upper oxide layer is formed by HTO or reoxidation of nitride. Thethickness of the upper oxide layer, for example, may be about 60 Å. Theupper oxide layer may be formed using the same techniques as for thelower oxide layer. For example, the isolation layer 448 has a thicknessof about 190 Å electrically. Other suitable thicknesses for the variouslayers and other suitable types of isolation layers may also be useful.For example, the middle nitride layer of the ONO stack may be replacedby high-K dielectric materials such as Al₂O₃, HbOx, TaOx and others. Theisolation layer, in one embodiment, serves to separate the first gateelectrode layer from a second gate electrode layer formed later and toseparate the second gate electrode layer from the substrate.Furthermore, the isolation layer which will be patterned later alsoserves as a charge storage layer for the memory cell.

A second gate electrode layer 433 is formed over the isolation layer andthe substrate. The second gate layer, for example, includes a blanketgate layer. In one embodiment, the second gate layer includespolysilicon. The second gate electrode layer can be formed by CVD. Thesecond gate electrode layer may be doped or in-situ doped with dopantssuch as phosphorus to form a doped polysilicon to impart a higherconductivity to the gate. The polysilicon layer, for example, includes aheavily doped polysilicon layer having phosphorus dopants and a dopantconcentration of about 10²⁰ atom/cm³. The thickness of the second gateelectrode layer, for example, may be about 1000 Å. Other materials,dopant concentrations and techniques and thickness ranges may also beuseful so long as it prevents poly depletion, reduce resistance andreduces voltage drop. An anneal may be performed after doping the secondgate electrode layer.

The process continues to form control gate 133 of the memory cell.Referring to FIG. 4 d, the second gate electrode layer and the isolationlayer beneath it are patterned. For example, a mask layer (not shown) isdeposited on top of the second gate layer. A hard mask layer 419, suchas an ARC layer may be provided between the mask and second gateelectrode layer. In one embodiment, the ARC layer is a Si-rich ARClayer. Other suitable types of hard mask or ARC layers may also beuseful. The mask is patterned as desired to serve as a control gatemask. For example, the mask is patterned to expose the second gateelectrode layer in the LV, MV and HV regions to be removed. The mask isalso patterned to expose portions of the second gate electrode layer inthe memory cell region. The exposed second gate layer and the isolationlayer beneath it are removed, leaving a portion of the second gateelectrode layer 133 and isolation layer 148 in the memory region whichforms the control gate as shown in FIG. 4 d. Removal can be achievedusing, for example, RIE. Other techniques may also be useful. As shown,the control gate is adjacent to the select gate and overlaps a portionof the select gate. For example, a portion of the control gate partiallyoverlaps a portion of the select gate, leaving a portion of the selectgate uncovered by the control gate while a portion of the control gateis disposed over the substrate. In one embodiment, the width of theoverlap portion of the control gate over the select gate is about 10-20nm while the width of the portion of the control gate above thesubstrate is about 100 nm. Other suitable width dimensions may also beuseful.

The process continues by removing the hard mask layers 417 and 419. Inone embodiment, the hard mask layers are removed by RIE. Other suitabletechniques may also be used to remove the hard mask layers. The removalof the hard mask layers exposes top surfaces of the first gate electrodelayer 430 in the LV, MV and HV regions and the top surface of thecontrol gate and a portion of the top surface of the select gate asshown in FIG. 4 e. A portion of the hard mask layer 417 remains,overlapping a portion of the select gate and under a portion of thecontrol gate.

Referring to FIG. 4 e, a soft mask layer 451 is provided over thesubstrate. The soft mask is patterned to form openings to expose thesecond sub-regions of the LV, MV and HV regions 102 ₂, 104 ₂ and 106 ₂.In one embodiment, the exposed first gate electrode layer in thesesub-regions may be doped with dopants such as phosphorus to form a dopedpolysilicon. The polysilicon layer, for example, includes a heavilydoped polysilicon layer having phosphorus dopants with a dopantconcentration of about 10²⁰ atom/cm³. Other suitable dopants and dopantconcentrations may also be useful so long as it prevents poly depletion,reduce resistance and reduces.

Referring to FIG. 4 f, a mask layer (not shown) is formed on thesubstrate and patterned. The mask layer is patterned to expose portionsof the first gate electrode layer 430 to be removed in the LV, MV and HVregions. The mask layer, for example, protects at least portionscorresponding to gates of the LV, MV and HV transistors 132, 134 and136. For example, the mask serves as a logic and peripheral gate mask.The exposed portions of the first gate electrode layer 430 are removedto form the gate electrodes of LV, MV and HV transistors as shown inFIG. 4 f. Removal can be achieved using, for example, RIE. The etch ispreferably selective to the gate dielectrics. Other techniques may alsobe useful.

The process continues to form first and second extension or lightlydoped diffusion (LDD) regions on the substrate adjacent to the MV gates134 in the MV region 104. In one embodiment, dopants of the oppositetype as the type of the well are implanted. In the case of a first typeMV well 114 b, the LDD regions 154 b include a second type. The LDDregions 154 a-154 b, for example, are formed using techniques such asion implantation and implant masks (not shown). For illustration, n-typedopants are implanted to form the LDD regions for a p-type MV well whilep-type dopants are implanted to form LDD regions for a n-type MV well.For example, n-type dopants, such as As, P, etc., or a combinationthereof, are implanted into p-type MV well. The LDD regions, forexample, are implanted with first or second type dopants having a dopantconcentration of about 10¹⁷ atom/cm³ and to a depth of about 2000 Å fromthe first substrate surface. Other concentrations or depth dimensionsmay also be useful.

Referring to FIG. 4 f, a LDD region 158 is formed in the substrateadjacent to the select gate 138 of the memory cell in the memory cellregion 108. In one embodiment, dopants of the opposite type as the typeof the memory cell well are implanted. In the case of a first typememory cell well 118, the LDD region 158 includes a second type. The LDDregion 158, for example, is formed using techniques such as ionimplantation and an implant mask (not shown) which exposes only thesubstrate region adjacent to the select gate while covering the LV, MV,HV regions and substrate or source region adjacent to the control gate.For example, n-type dopants, such as phosphorus and boron, are implantedinto p-type memory cell well. The LDD region 158, for example, is formedby implanting second type dopants having a dopant concentration of about10¹⁷ atom/cm³ and to a depth of about 3000-4000 Å from the firstsubstrate surface. Other suitable concentrations or depth dimensions mayalso be useful.

Refer to FIG. 4 g, the process continues to form LDD regions 152 a-152 bon the substrate adjacent to the LV gates 132 in the LV region 102. Inone embodiment, dopants of the opposite type as the type of the well areimplanted. In the case of a first type LV well 112 b, the LDD regions152 b include a second type. The LDD regions 152 a-152 b, for example,are formed using techniques such as ion implantation and implant masks.For illustration, n-type dopants are implanted to form the LDD regionsfor a p-type LV well while p-type dopants are implanted to form LDDregions for a n-type LV well. For example, n-type dopants, such as As,P, etc., or a combination thereof, are implanted into p-type LV well.The LDD regions, for example, are implanted with first or second typedopants having a dopant concentration of about 10¹⁷ atom/cm³ and to adepth of about 2000 Å from the first substrate surface. Other suitableconcentrations or depth dimensions may also be useful.

The process continues to form first and second spacer elements onsidewalls of the gates. Referring to FIG. 4 g, a first spacer layer isformed over the gates and substrate. The first spacer layer, forexample, includes a dielectric material such as oxide. Other materialsmay also be used. The first spacer layer, for example, is formed bydepositing a blanket first dielectric layer on the substrate and thegates. The first spacer layer is then patterned to form L-shaped spacers172. Removal can be achieved, for example, using an anisotropic etch,such as RIE. The thickness of the first spacer elements, for example, isabout 300-1000 Å. The process continues to form second spacer elements174. A second spacer layer is formed over the over the first spacerelements, top of the gates and substrate. The second spacer layer, forexample, includes a dielectric material such as nitride. Other materialsmay also be used. The second spacer layer, for example, is formed bydepositing a blanket second spacer layer on the substrate and is thenpatterned to remove the horizontal portions. Removal can be achieved,for example, using an anisotropic etch, such as RIE. Second spacerelements 174 are formed on the first spacer elements 172 as shown inFIG. 4 g. The thickness of the second spacer elements as formed, forexample, is about 200-800 Å. Other thicknesses are also useful. Asshown, two spacer elements are formed adjacent to each gate sidewall. Inother embodiments, it is understood that forming one spacer element oneach gate sidewall may also be useful.

In FIG. 4 g, first and second heavily doped diffusion regions orsource/drain (S/D) regions 162 a-162 b, 164 a-164 b, 166 a-166 b and 168are formed on the substrate adjacent to the LV, MV, HV and memory gates.In one embodiment, dopants of the opposite type as the type of the wellare implanted. In the case of a first type memory cell well, thediffusion regions include a second type. The heavily doped diffusionregions, for example, are formed using techniques such as ionimplantation. For illustration, n-type dopants are implanted to form thefirst and second heavily doped diffusion regions for a p-type memorycell well. For example, n-type dopants, such as P, As, etc., or acombination thereof, are implanted into p-type memory cell well. In oneembodiment, the p-type memory cell well 118, for example, is implantedwith n-type dopants, such as Arsenic, having a dopant concentration ofabout 10¹⁹-10²⁰ atom/cm³ and to a depth of about few thousand Å from thefirst substrate surface to form the heavily doped S/D regions 168 whichhave depths deeper than depths of the LDD region 158 and counter dopedregions 128.

The process continues by performing a cleaning process to remove gatedielectric layers over S/D regions and residues over the gates beforeperforming a silicidation process. In one embodiment, the silicidationprocess forms silicide contacts (not shown) on, for example, exposedportions of the contact regions, such as S/D regions and the gates. Thesilicide contacts, for example, may be nickel-based silicide contacts.Other types of metal-based silicide contacts, such as titanium orcobalt-based silicide contacts, may also be useful. Due to the overlaymargin, the silicide contacts are displaced from the adjacent gates. Forexample, the silicide contacts are displaced from sides of gates of thesplit gate by the spacer 174. The displacement from sides of gatesshould be sufficient to prevent bridging with the gates.

In one embodiment, silicide contacts are formed by depositing a metallayer on the substrate. An anneal is performed to cause a reaction withexposed portions of the S/D regions and the gates. The reaction formssilicide contacts on the exposed portions of these regions. Unreactedmetal are selectively removed, leaving the metal-based silicide contactson the exposed portions of these regions. Removing unreacted metal maybe achieved using, for example, a wet etch. Other techniques forremoving the unreacted metal may also be useful.

The process continues by forming interconnections to the S/D regions andgates of the transistors. For example, an ILD layer 181 is depositedover the substrate as shown in FIG. 4 h and contacts 183 are formedthrough the ILD layer to form interconnections. Contacts 183 are formedthrough the ILD layer 181 to the contact regions, such as S/D regionsand gates, through mask and etch technique. The ILD layer is patternedto form contact openings and the contact openings are filled withconductive material, such as tungsten, to form the contacts 183. Thediffusion regions and gates, for example, are appropriately coupled toSLs, BLs, SGLs and CGLs or WLs. Additional processes are performed tocomplete the IC. These processes include, for example, finalpassivation, dicing and packaging.

The process as described in FIGS. 4 a-4 h enables a memory cell 198 suchas that shown in FIG. 1 a to be formed. Thus, advantages of the memorycell 198 will not be described or described in detail. Further, theprocess as described in FIGS. 4 a-4 h is highly compatible with CMOSlogic processing technology. For example, the memory cell 198 can beeasily integrated into existing or other logic processing technologiesand formed together with LV, MV and HV devices. The process as describedoffers a simplified and low costs embedded NVM solution. All it requiresis the use of additional mask layers to form the memory cell togetherwith other logic devices without the need to purchase new equipment. Inaddition, the process margin in the memory region is improved due tomuch smaller memory cell structure, such as 1.5T, relative toconventional 2T cell structure, thus potentially shrinks the cell sizefurther. Further, as described, the process allows a memory cell 198having asymmetrical S/D regions or junctions to be formed. For example,the drain region of the memory cell includes counter doped region, LDDregion and heavily doped drain region while the source region of thememory cell includes counter doped region, heavily doped source regionand is devoid of LDD region. By providing counter doped regions, onlyone mask is required to achieve the asymmetrical S/D regions for thememory cell and allows for optimization of individual Vth for the selectgate portion to improve the short channel effect (SCE) and the controlgate portion to improve programming efficiency. This offers a simplifiedsolution and reduces the manufacturing costs compared to conventionaltechnique which necessarily uses two separate implant masks to formasymmetrical S/D regions.

FIGS. 5 a-5 g show cross-sectional views of another embodiment of aprocess 500 for forming a portion of a device. In one embodiment, theprocess 500 forms the portion of the device 200 in the memory cellregion 108 as shown in FIG. 2. The process may contain similar steps asthat described in FIGS. 4 a-4 h. In the interest of brevity, commonelements having the same reference numerals may not be described ordescribed in detail. Although only the memory cell region 108 is shown,it is understood that the substrate includes other regions as describedin FIG. 4 a. As shown in FIG. 5 a, a partially processed substrate isprovided. The partially processed substrate is similar to that describedin FIG. 4 a. For example, the substrate is processed to form the memorycell well 118, the second gate dielectric layer 124 which is formedsimultaneously in the MV region which also serves as the select gatedielectric which will be described later and is processed up to thestage of forming a first gate electrode layer 430 over the substrate.

In one embodiment, the process continues to form a hard mask layer 517over the substrate and the first gate electrode layer 430. The hard masklayer, in one embodiment, includes a nitride layer. Various suitabletechniques, such as CVD, may be used to form the hard mask layer. Thethickness of the hard mask layer, for example, is about 30 nm. Othersuitable thicknesses may also be useful so long as it is sufficientlythick to serve as an etch stop layer as well as to elevate the height ofthe control gate such that larger spacer can be formed later to avoidshorting between the select and control gates as will be describedlater. A soft mask layer (not shown), for example, which includes aphotoresist is provided over the hard mask layer. To improvelithographic resolution, an ARC layer 617 may be provided between themask and hard mask layer. In one embodiment, the ARC layer is a Si-richARC layer. Other suitable types of ARC layer may also be useful. UnlikeFIG. 4 a, the soft mask is patterned to serve as an intermediate gatemask. For example, the mask is patterned to expose portions of the firstgate electrode and hard mask layers in the memory cell region to beremoved. As such, the exposed portions of the first gate electrode, ARCand hard mask layers which are not protected by the intermediate gatemask over the memory cell region are removed. Removal of the exposedportions can be achieved using, for example, RIE. Other techniques mayalso be useful. The portion of the first gate electrode, ARC and hardmask layers protected by the mask in the memory cell region remains,forming an intermediate structure as shown in FIG. 5 b. Referring toFIG. 5 b, the intermediate structure, in one embodiment, includes awidth W₂ which is at most 2 times the width of a select gate to beformed and a gap between the select gates having a size of at least 2for more (where f is the minimum technology node feature size). Forexample, the width of the intermediate structure W₂ is equal to about2×W_(SL)′+2f or more, where W_(SL)′ is smaller than W_(SL) as describedin FIG. 4 b which is formed or defined by lithographic technique and fis the minimum technology node feature size. The width W₂, for example,is about 300-400 nm. Other suitable width dimensions may also be usefulas long as it allows for two memory cells to be formed later withouthaving select and control gates overlay issue.

Referring to FIG. 5 c, the process continues to form an isolation layer448 over the substrate. A second gate electrode layer 433 is thenblanket deposited over the isolation layer 448 as shown in FIG. 5 d. Theisolation layer 448 and the second gate electrode layer 433 as shown inFIGS. 5 c-5 d, for example, include the same material and are formed bythe same technique as that described in FIG. 4 c. Thus, details of thematerials and techniques for the isolation and second gate electrodelayers will not be described. In one embodiment, control gates 233 areformed by anisotropically etching the second gate electrode layer 433.The etch removes horizontal portions of the second gate electrode layer433 and stops when it reaches the isolation layer 448, leaving spacersto serve as the control gates 233. The etch exposes portions of theisolation layer 448 on the substrate and on top of the intermediatestructure. As shown, the control gates are disposed adjacent to thesidewalls of the intermediate structure and do not overlap theintermediate structure.

The process continues to pattern the intermediate structure to defineselect gate electrodes 138 of first and second memory cells. To definethe select gate electrodes of first and second memory cells, a mask 511is provided on the substrate as shown in FIG. 5 e. The mask 511, forexample, includes a photoresist. The mask 511, for example, includes anopening having a width W_(O1) which exposes portions of the intermediatestructure to be removed. In one embodiment, the width W_(O1) of the maskshould be sufficiently wide to form an opening which allows a borderedcontact which lands directly on the drain region to be formed thereinand sufficiently isolated from adjacent select gates to preventelectrical shorts between adjacent memory cells. For example, the widthW_(O1) is at least the size of 2f or more (where f is the minimumtechnology node feature size). The width W_(O1), for example, is about150 nm. Other suitable width dimensions may also be useful. The removalprocess, in one embodiment, includes RIE to remove the exposed portionsof the isolation, ARC and hard mask and first gate electrode layers ofthe intermediate structure. Various etch chemistries may be employed toremove the layers. Other suitable types of removal processes may also beemployed. The etch stops when it reaches the gate dielectric layer 124as shown in FIG. 5 f.

As shown in FIG. 5 f, the first and second memory cells 298 ₁ and 298 ₂are defined. The process continues to form a shallow and lightly dopeddrain region 158. A wet clean process may be performed to remove anyunwanted residue before forming the lightly doped drain region 158. Inone embodiment, dopants of the opposite type as the type of the memorywell are implanted. In the case of a first type memory cell well, thelightly doped drain region 158 include a second type. The lightly dopeddrain region 158, for example, is formed using techniques such as ionimplantation which is self-aligned to the gates without using a separateimplant mask. For illustration, n-type dopants are implanted to form theshallow drain region 158 for a p-type memory cell well. For example,n-type dopants are implanted into exposed portion of the substrateadjacent to the select gate electrodes 138 between the first and secondmemory cells. The implantation process employs a low energy and dose toform the shallow drain region 158 identical to the lightly doped drainregion 158 as described in FIG. 4 f. For example, the exposed portion ofthe substrate between the first and second memory cells, for example, isimplanted with energy of about 30-40 keV with phosphorus dopants havinga dopant concentration of about 10¹⁷ atom/cm³ and to a depth of about3000-4000 Å from the first substrate surface. In some cases, the LDDregions 158 may incorporate low dose of boron (B) as halo implant tosuppress short channel effect. As shown in FIG. 5 f, the shallow drainregion 158 is a common drain region for the first and second memorycells. The mask 511 is removed after forming the shallow drain region158.

The process continues to remove horizontal portions of the isolationlayer 448 over the ARC layer 617, the ARC layer 617 and the hard mask517 as shown in FIG. 5 g. The removal of these layers can be achievedusing, for example, RIE. Other suitable techniques may also be employedto remove these layers. The etch stops until it exposes top surface ofthe select gate electrodes 138 as shown in FIG. 5 g. Sidewall oxides 572are selectively grown on the select and control gates 138 and 233 afterthe RIE process. The sidewall oxides 572, for example, include an oxide.The oxide is formed using high temperature wet oxidation to repairplasma damage caused by the RIE process. The high temperature wetoxidation may be performed, for example, at 900° C. Other temperaturemay also be useful. The thickness of the sidewall oxides 572 is about200 Å. Other thickness ranges may also be useful.

The process continues to form LDD regions 258 in the substrate adjacentto the control gate of the memory cell in the memory cell region 108. Inone embodiment, dopants of the opposite type as the type of the memorycell well are implanted. In the case of a first type memory cell well118, the LDD regions 258 includes a second type. The LDD regions 258,for example, are formed using techniques such as ion implantation and animplant mask (not shown) which exposes only the substrate regionadjacent to the control gates. For example, n-type dopants, such asphosphorus and boron, are implanted into p-type memory cell well. TheLDD region 258, for example, is formed by implanting second type dopantswith energy of about 50-60 keV having a dopant concentration of about10¹⁷ atom/cm³ from the first substrate surface. Other suitableconcentrations or depth dimensions may also be useful. As shown, the LDDregion 258 is deeper than the shallow drain region 158.

First and second heavily doped diffusion or S/D regions 168 are alsoformed in the substrate adjacent to the memory gates. The techniques andparameters for forming the heavily doped S/D regions 168 are the same asthat described in FIG. 4 g. Thus, these techniques and parameters willnot be described.

The process may continue to complete forming the device. For example,the process continues to define the LV, MV and HV gates in the logicregion, which is the same as that described in FIG. 4 f. Further, theprocess continues until a portion of the device shown in FIG. 5 g isformed. For instance, the process continues to form first and secondsidewall spacers 172 (not shown) and 174, silicide contacts 531, ILDlayer 181, contacts 183 etc. Techniques and materials of these featuresare the same as that already described in FIGS. 4 g-4 h. Additionalprocesses may be performed, including forming LDD and S/D regions of thelogic devices, forming one or more interconnect levels, finalpassivation, dicing, assembly and packaging.

The process as described in FIGS. 5 a-5 g enables a memory cell 200 suchas that shown in FIG. 2 to be formed. Thus, advantages of the memorycell 200 will not be described or described in detail. The process asdescribed in FIGS. 5 a-5 g also offers similar or the same advantages asthe process as described in FIGS. 4 a-4 h. Furthermore, as described,the control gate 233 is a control gate spacer formed by RIE spacerprocess which does not require an etch mask or high selective etch. Asshown, the process described above only forms a control gate spacer 233on one side of a select gate. This is in contrast to conventionalprocess where control gates will be formed on both sides of a selectgate and an expensive lithography mask is necessarily required to removethe control spacers over the drain region prior to forming the drainregion. Thus, the process as described in FIGS. 5 a-5 g eliminates theneed of an expensive lithography mask and offers a cost saving solution.Moreover, since the memory cell 298 includes control gate spacer, thememory cell can be shrunk further. In addition, the process allows for amemory cell 298 having asymmetrical S/D regions to be formed with theuse of a single mask. For example, the process enables a shallowself-aligned drain region 158 which does not require an additional orseparate implant mask to be formed; and the single implant mask whichexposes the source region while covering the drain region allows lightlydoped source regions 258 which are formed by different dose and energythan that of shallow drain region 158 to be achieved. The shallow drainregion 158 is advantageous as it allows smaller gates to be formed whilesuppressing short channel effect and the deeper source region thatusually comes with higher source junction breakdown is highly desirablefor programming. Thus, this process produces smaller memory cell,optimizes the device performance and reduces manufacturing costs at thesame time.

FIGS. 6 a-6 f show cross-sectional views of another embodiment of aprocess 600 for forming a portion of a device. In one embodiment, theprocess 600 forms the portion of the device 300 in the memory cellregion 108 of the device as shown in FIG. 3. The process may containsimilar steps as that described in FIGS. 4 a-4 h and FIGS. 5 a-5 g.Further, the process as will be described below allows the memory cellto shrink further. In the interest of brevity, common elements havingthe same reference numerals may not be described or described in detail.Although only the memory cell region 108 is shown, it is understood thatthe substrate includes other regions as described in FIG. 4 a. As shownin FIG. 6 a, a partially processed substrate is provided. The partiallyprocessed substrate is similar to that described in FIG. 5 d. Forexample, the substrate is processed to form the memory cell well 118,the second gate dielectric layer 124 which is formed simultaneously inthe MV region which also serves as the select gate dielectric which willbe described later and is processed up to the stage of forming thecontrol gates 233 as described in FIG. 5 d.

In this embodiment, the intermediate structure includes a width W₃ whichis at least 2 times the width of a select gate W_(SL)′ as defined aboveto be formed and a gap between the select gates having a size of lessthan 2f (where f is the minimum technology node feature size). Thus, thewidth of the intermediate structure W₃ in this embodiment is smallerthan the width of the intermediate structure W₂ described in FIG. 5 b.In one embodiment, the process continues to pattern the intermediatestructure to define select gate electrodes 138 of first and secondmemory cells. To define the select gate electrodes of first and secondmemory cells, a mask 611 is provided on the substrate as shown in FIG. 6a. The mask 611, for example, includes a photoresist. The mask 611, forexample, includes an opening having a width W_(O2) which exposesportions of the intermediate structure to be removed. In one embodiment,the width W_(O2) of the mask 611 is smaller than the width W_(O1) of themask 511 as described in FIG. 5 e. In one embodiment, the width W_(O2)of the mask 611 is less than the size of 2f (where f is the minimumtechnology node feature size). The width W_(O2), for example, is about1.2 to 1.5f. The width W_(O2), for example, is about 80 nm. Othersuitable width dimensions may also be useful. A removal process, in oneembodiment, which includes RIE is used to remove the exposed portions ofthe isolation, ARC and hard mask and first gate electrode layers of theintermediate structure. Various etch chemistries may be employed toremove the layers. Other suitable types of removal processes may also beemployed. The etch stops when it reaches the gate dielectric layer 124as shown in FIG. 6 a.

As shown in FIG. 6 a, the first and second memory cells 398 ₁ and 398 ₂are defined. The process continues to form a shallow drain region 158.The shallow drain region 158 is formed using the same dopants andtechnique as that described in FIG. 5 f. In one embodiment, the drainregion is self-aligned to the gates and is a shallow drain region. Thus,in this embodiment, the width of drain region is further reduced as thespacing between adjacent select gates is reduced. As shown, the shallowdrain region 158 is a common drain region for the first and secondmemory cells.

The process continues to remove horizontal portions of the isolationlayer 448 over the ARC layer 617. The removal of the horizontal portionof the isolation layer 448 over the ARC layer 617 can be achieved using,for example, RIE. Other suitable techniques may also be employed toremove this portion. The etch stops until it exposes top surface of theARC layer 617 as shown in FIG. 6 b. Sidewall oxides 572 are selectivelygrown on the select and control gates 138 and 233. Heavily dopeddiffusion regions 168 are formed adjacent to the control gates 233. Thematerial, dopants and techniques for forming the sidewall oxides 572 andheavily doped diffusion regions 168 are the same as that described inFIG. 5 g.

Referring to FIG. 6 b, the process continues to form an insulator layer631 over the substrate. The insulator layer, for example, is a conformallayer which is deposited over the substrate. In one embodiment, theinsulator layer includes an ozone-TEOS layer or HARP oxide. Othersuitable insulator material which can completely fill the gap betweenadjacent select gates and does not cause plasma damage may also be used.

A mask (not shown) is provided over the substrate. The mask includes anopening which exposes the memory cell region 108 while covering thelogic and peripheral region. In one embodiment, the process continues byanisotropically etching the insulator layer 631. The etch removeshorizontal portions of the insulator layer 531, leaving verticalportions of the insulator layer 631 disposed over the first spacerelements 572 adjacent to the select gates 130 to serve as insulatorliners 631 and to define the location of which a contact plug is to beformed later. The etch also removes portions of the gate dielectriclayer 124 over the drain region and source regions.

Referring to FIG. 6 c, the process continues to form a dummy layer 633over the substrate and fills the space between the insulator linersabove the drain region. The dummy layer, for example, includes a blanketdummy layer. In one embodiment, the dummy layer includes polysilicon.The dummy layer can be formed by CVD. Other suitable materials andtechniques may be used for the dummy layer. The thickness of the dummylayer is, for example, about 100 Å. Other thickness ranges may also beuseful.

A planarization process is performed on the substrate such that the topsurface of the various layers are substantially planar or flat as shownin FIG. 6 d. For example, a chemical mechanical polishing (CMP) processmay be employed. Other types of planarization processes may also beuseful. In one embodiment, the planarization process stops when itreaches top surface of the hard mask layer 517. An over polishingprocess may be performed to thin the hard mask layer. For example, thehard mask layer is reduced to about 5 nm thick. Other suitable thicknessdimension may also be useful. As shown in FIG. 6 d, the remaining dummylayer between the insulator liners 631 is directly over and coupled tothe drain region, forming a contact plug 633. Thus, the contact plug 633is self-aligned and made borderless to the drain region withoutrequiring critical lithography process to define the contact plug.

Referring to FIG. 6 e, the process continues by providing a mask layer(not shown). The mask layer, for example, includes openings which exposethe logic and peripheral region and source regions of the memory cellregion 108 which are adjacent to the control gates while coveringportions of the memory cell region over the drain region which areadjacent to the select gates. In one embodiment, the process continuesto remove the remaining dummy layer 633 over the source regions. In oneembodiment, the dummy layer 633 over the source regions is removed by,for example, a RIE process. Other suitable techniques may also beemployed to remove the dummy layer 633 over these regions. As shown, thecontact plug 633 is protected by the mask layer and remains over thedrain region.

The process may continue to complete forming the device. For example,the process continues to define the LV, MV and HV gates in the logic andperipheral region, which is the same as that described in FIG. 4 f.Further, the process continues until a portion of the device shown inFIG. 6 f is formed. For instance, the process continues to form firstand second sidewall spacers 172 (not shown) and 174, silicide contacts531, ILD layer 181, contacts 183 and 184, etc. Techniques and materialsof these features are the same as that already described in FIGS. 4 g-4h. Prior to the silicidation process, the remaining hard mask 517 overthe select gates is removed using suitable technique. In one embodiment,the contact 184 over the drain region is indirectly coupled to the drainregion through the contact plug 633. The contact 184 is formed by thesame technique used to form contacts 183. Additional processes may beperformed, including forming LDD and S/D regions of the logic devices,forming one or more interconnect levels, final passivation, dicing,assembly and packaging.

The process as described in FIGS. 6 a-6 f enables a memory cell 398 suchas that shown in FIG. 3 to be formed. Thus, advantages of the memorycell 398 will not be described or described in detail. The process asdescribed in FIGS. 6 a-6 f also offers similar or the same advantages asthe process as described in FIGS. 4 a-4 h or FIGS. 5 a-5 g. Furthermore,the process as described above enables a self-aligned and borderlessdummy contact plug to be formed and directly coupled to the drain regionwithout requiring critical lithography process. As a result, theembodiment as described with respect to FIGS. 6 a-6 f removes thelimitation faced by critical lithography which requires the patternedphotoresist mask having at least 2 times the minimum technology featuresize in order to define the contact to the drain region, such as thatshown in FIG. 2. Since self-aligned contact plug can be formed betweenthe adjacent select gates, the space between the adjacent select gatescan be reduced further, resulting in even smaller drain region andmemory cell to be formed. In addition, the insulator liners 631 alsoavoid shorting between the contact plug with adjacent select gates,thereby increasing reliability of the memory cell.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments, therefore, are to be considered in all respectsillustrative rather than limiting the invention described herein. Scopeof the invention is thus indicated by the appended claims, rather thanby the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are intended to beembraced therein.

What is claimed is:
 1. A method for forming a semiconductor devicecomprising: providing a substrate prepared with a memory cell region;forming a first gate structure on the memory cell region; forming anisolation layer on the substrate and over the first gate structure;forming a second gate structure, wherein the second gate is adjacent toand separated from the first gate structure by the isolation layer;processing the first and second gate structures to form at least onesplit gate structure with first and second adjacent gates; and providingasymmetrical source and drain regions adjacent to first and second sidesof the split gate structure.
 2. The method of claim 1 wherein: thesubstrate comprises silicon; the first gate comprises a select gate; thesecond gate comprises a control gate; and the isolation layer comprisesan oxide-nitride-oxide (ONO) stack to form a split gate SONOS memorycell.
 3. The method of claim 1 comprising providing a hard mask over thefirst gate structure prior to forming the isolation layer.
 4. The methodof claim 3 wherein providing asymmetrical source and drain regionscomprises: forming counter doped regions into regions of the substrateadjacent to the sides of the patterned first gate with blanketimplantation with no added lithographic mask; providing an implant maskto cover the region of the substrate adjacent to the second gate andperforming an implant to form lightly doped diffusion (LDD) regionadjacent to the first gate; and forming heavily doped regions intoregions of the substrate adjacent to sides of the split gate structure,wherein the heavily doped region includes a depth deeper than thecounter doped regions and LDD region.
 5. The method of claim 3 whereinprocessing the second gate structure forms the second gate having afirst portion which partially overlaps a portion of the first gate and asecond portion over the substrate.
 6. The method of claim 5 wherein aportion of the hard mask layer over the first gate structure is removedwhile a portion of the hard mask under the portion of the second gateoverlapping the first gate remains after processing the second gatestructure.
 7. The method of claim 3 comprises forming an anti-reflectivecoating (ARC) layer over the hard mask layer, wherein the first gatestructure, the hard mask and the ARC layers form an intermediatestructure.
 8. The method of claim 7 wherein processing the first andsecond gate structures comprises anisotropically etching the second gatestructure, wherein the etch removes horizontal portions of the secondgate structures to form second gate spacers over first and second sidesof the intermediate structure.
 9. The method of claim 8 whereinprocessing the first and second gate structures comprises: providing amask having an opening with a width of at least 2f or more over thesubstrate, wherein f is the minimum technology node feature size; andpatterning the intermediate structure to form at least first and secondsplit gate structures, wherein each of the split gate structurecomprises first gate and second gate spacer adjacent to the first gatewhile leaving a gap having a width of at least 2f or more between thefirst and second split gate structures.
 10. The method of claim 9wherein providing asymmetrical source and drain regions comprises:forming a lightly doped drain region in a region of the substratebetween first and second split gate structures, wherein the lightlydoped drain region is formed by an implantation which is self-aligned tothe split gate structures without using an implant mask; and forminglightly doped regions into regions of the substrate adjacent to sides ofthe second gate spacers of the split gate structure, wherein the lightlydoped regions are formed by an implantation which employs an implantmask and with higher dose and energy compared to that of the lightlydoped drain region.
 11. The method of claim 10 comprises removing theARC and hard mask layer after providing the asymmetrical source anddrain regions, wherein the first and second gates of the split gatestructure comprise non-coplanar top surfaces.
 12. The method of claim 8wherein processing the first and second gate structures comprises:providing a mask having an opening with a width of less than 2f over thesubstrate, wherein f is the minimum technology node feature size; andpatterning the intermediate structure to form at least first and secondsplit gate structures, wherein each of the split gate structurecomprises first gate and second gate spacer adjacent to the first gatewhile leaving a gap having a width of less than 2f between the first andsecond split gate structures.
 13. The method of claim 12 whereinproviding asymmetrical source and drain regions comprises: forming alightly doped drain region in a region of the substrate between firstand second split gate structures, wherein the lightly doped drain regionis formed by an implantation which is self-aligned to the split gatestructures without using an implant mask; and forming lightly dopedregions into regions of the substrate adjacent to sides of the secondgate spacers of the split gate structure, wherein the lightly dopedregions are formed by an implantation which employs an implant mask andwith higher dose and energy compared to that of the lightly doped drainregion.
 14. The method of claim 13 comprising: providing an insulatorlayer over the substrate, wherein the insulator layer completely fillsthe gap between the first and second split gate structures; andanisotropically etching the insulator layer, leaving vertical portionsof the insulator layer as insulator liners disposed over sides of thefirst gates of the split gate structures adjacent to the drain region.15. The method of claim 14 comprising forming a borderless contact plugover the drain region, wherein the borderless contact plug is formed by:providing a dummy layer over the substrate and fills the space betweenthe insulator liners over the drain region; performing a planarizationprocess such that top surfaces of the first and second gates and thecontact plug are substantially coplanar with each other.
 16. Asemiconductor device comprising: a substrate having a memory cellregion; a first gate disposed on the memory cell region; an isolationlayer disposed on the substrate and over the first gate; a second gate,wherein the second gate is adjacent to and separated from the first gateby the isolation layer and the first and second gates correspond to asplit gate structure; and asymmetrical source and drain regions adjacentto first and second sides of the split gate structure.
 17. Thesemiconductor device of claim 16 wherein: the substrate comprisessilicon; the first gate comprises a select gate; the second gatecomprises a control gate; and the isolation layer comprises anoxide-nitride-oxide (ONO) stack to form a split gate SONOS memory cell.18. The semiconductor device of claim 17 wherein: the drain region isdisposed adjacent to the select gate and the source region is disposedadjacent to the control gate; the drain region is coupled to a bit line(BL), the source region is coupled to a source line (SL), the selectgate is coupled to a select gate line (SGL) and the control gate iscoupled to a control gate line together forming a word line, resultingin standard sensing configuration in NOR architecture with common sourcewithin a sector and different source bias across sectors.
 19. Thesemiconductor device of claim 17 wherein: the source region is disposedadjacent to the select gate and the drain region is disposed adjacent tothe control gate; the source region is coupled to a source line (SL),the drain region is coupled to the a bit line (BL), the select gate iscoupled to a select gate line (SGL) and the control gate is coupled to acontrol gate line together forming a word line, resulting in sourcesensing configuration in NOR architecture with common source.
 20. Thesemiconductor device of claim 16 wherein the asymmetrical source anddrain regions comprise counter doped regions in regions of the substrateadjacent to first and second sides of the split gate structure, a lightdoped diffusion region in a region adjacent to the first gate andheavily doped regions having a depth deeper than the counter dopedregions disposed adjacent to first and second sides of the split gatestructure.
 21. The semiconductor device of claim 16 wherein theasymmetrical source and drain regions comprise a lightly doped drainregion which is shallow adjacent to the first gate and a lightly dopedregion disposed adjacent to the second gate which is deeper and heavilydoped than the lightly doped drain region.